The Icerune Crater is one of several city-relics on Sapience, and it can be found on the western side of the city of Cyrene. When empowered with the corpses of Lesser Eidolons spawned from the Fonts of other cities, the Icerune Crater is able to return Blu, the Guardian Dragon of Cyrene, to the city to help protect it.
The Icerune Crater was first used in this way to return Blu to Cyrene when he was abducted by the qlippah.